The present invention relates generally to the playback of audio using a general purpose computer.
There have been several attempts to distribute and communicate audio information in digital form, such as the Musical Instrument Digital Interface ("MIDI") and the Modular File Format ("MOD"). Each of these prior attempts, however, produces a format designed for a specific purpose, and none of them can distribute audio in a flexible, dynamic, and efficient way over a network. Furthermore, none of these prior attempts has addressed real-time three-dimensional audio sound.
MIDI was designed by manufacturers of electronic musical instruments as a digital communication standard between such instruments. Consequently, MIDI was first and foremost designed by and for the narrow market of the music industry, and not for a much wider market, such as the entertainment market or the communication market.
Initially, MIDI was used primarily for communication between digital musical instruments, such as synthesizers and drum machines. Later, as these instruments became more and more computer oriented, MIDI became increasingly used for communication between digital instruments and computers. This evolution gave rise to a wide range of software tools for handling MIDI information, such as the so-called sequencer programs which basically provide functions for recording, editing, and playback of MIDI data. The increased use of MIDI by computers created a need for a convenient file format for exchanging MIDI data between such computers. For this purpose, the standard MIDI file format was created and is widely used today.
The main advantages of MIDI are low memory usage, relatively simple and small specification, and wide acceptance. As a result, the MIDI standard is well suited for low cost implementation because it tends to require few resources.
The disadvantages of MIDI are many and are mostly due to the essentially linear format of MIDI, which incorporates little knowledge about the actual musical or acoustical content of the material. MIDI works exclusively with control information consisting of event triggering messages and does not use any information about the actual audio signal itself, except for being able to transmit a number which has been assigned to a sound bank in a particular sound device. The lack of the ability to store intelligent knowledge using the standard MIDI file format also makes MIDI inadequate for use as a format to store musical knowledge and as a description of dynamic audio.
Conventionally, an audio event can sound quite different from one computer to another depending on the type of hardware (e.g., sound cards) being used for audio playback. For example, most sound cards have a synthesizer with pre-defined sound banks which differ in quality and nature from one sound card to another. Non-limiting examples of conventional sound cards include: the Soundlaster 16 sound card manufactured by Creative Technology of Singapore; and the AWE32 and the AWE64 sound cards manufactured by Creative Technology Ltd. of Singapore. To play the audio stored in the sound card's synthesizer, MIDI is often used because of its standard communication language for music events. MIDI permits transmission of audio event signals but does not permit transmission of audio samples. With MIDI, there is no indication as to what the audio output will sound like because of the dependence on the synthesizer to which the MIDI signal is sent.
MOD, which was originally developed for the Amiga computer manufactured by Commodore, and which was extended to other computers, distributes instrument audio files. These audio files include associated event data and primarily include note on and off information. MOD is primarily a file format and is not a communication standard. MOD files are basically a hybrid between audio sample data files (e.g., the .wav file format) and audio sequence data files (e.g., MIDI control event files).
MOD files are useful for distributing the same sounding audio data from one platform to another without requiring as much memory as one large pure audio data file. MOD files, for example, are useful for distributing audio demonstrations more efficiently than a pure audio data file and are more reliable in terms of sound result than MIDI.
MOD advantageously provides for storage of more musical content knowledge than formats which either store only audio (e.g., the .wav file format) or only events (e.g., the standard MIDI file format). MOD also provides a better way for describing audio than MIDI files. Although MIDI can only describe audio with tracks, MOD can describe audio with both tracks and patterns. Patterns can be used to generate audio phrases, which are created once, used many times, and make economical use of both audio and event data.
The main disadvantage of MOD is that, although it has a richer format than MIDI, it is still, like MIDI, static and linear. Although MOD files are much smaller than pure audio data files, MOD files are relatively huge compared to most MIDI files because there is no way to separate the audio data from the event data. Further, MOD is neither a clearly defined nor well established standard because many different varieties of MOD are used and required for different audio players. Moreover, MOD is not as widely accepted and distributed as the MIDI standard.
To deliver audio over the Internet, there are currently numerous technologies which can be used. These products today send broadcasts of live radio stations and music samples to any Internet user. Current audio compression technology is able to send FM quality music in real time to any Internet user who has a reasonably fast modem (e.g., 14.4 Kb or 28.8 Kb). With an ISDN line or better, it is possible to receive compact disk ("CD") quality music. Bandwidth, however, is a limiting factor to distributing audio over the Internet, at least until the latest 56.6 Kb modem becomes widely available.
To transmit audio over the Internet, Real Audio and Liquid Audio are products currently available. Real Audio by Real Networks of Seattle, Wash., is the most popular audio streaming software for distribution of real time audio over the Internet today. It is used, for example, by the American Broadcasting Company ("ABC") and the Cable News Network ("CNN") to send live news over the Internet. With Real Audio, it is also possible to listen to radio stations from all over the world. The latest version can deliver broadcast quality stereo sound to 28.8 Kb modems and near CD quality sound to ISDN and LAN connections. The latest Real Audio player also supports Real Video, a technology which uses fractal based technology to send streaming video at 10 fps over ISDN connections. For more information, see http://www.realaudio.com and http://www.timecast.com.
The main disadvantages of Real Audio are that it is a noninteractive format that does not guarantee quality, and it is bandwidth expensive, especially for higher quality.
Liquid Audio, manufactured by Liquid Audio of Redwood City, Calif., consists of three products: mastering software; server software; and playback software. Liquid Audio should solve some significant problems in the commercial delivering of music over the Internet because it uses a two-layer protection mechanism. As the first layer, the purchased audio is encrypted so that it can only be played back on a computer having de-encrypting software. The second layer of Liquid Audio uses a digital watermarking technology that identifies the purchaser of the piece of audio. The second layer of protection is used if the first layer of protection is penetrated. The Liquid Audio software uses compression technology from Dolby Laboratories, Inc. of San Francisco, Calif., to deliver CD quality music. The Liquid Audio format also has support for graphics, lyrics, linear notes, and production information. For more information, see http://www.liquidaudio.com.
The main disadvantages of Liquid Audio are that it is noninteractive and essentially not real-time. Further, Liquid Audio is mainly an anti-piracy format.